The loss of food culture in the US is partly to blame. All of the loopy fad diets people are describing here are a symptom of the same larger problem that has caused the obesity epidemic. There is no shortage of intact culinary cultures in the world that include wonderful, healthy, inexpensive things that anybody can prepare with a little time and love. Accordingly, your best bet for good, cheap produce and healthy stuff in a big city is any immigrant/ethnic market. These usually depend on parallel supply chains that allow them to undercut and outperform mainstream supermarkets.